The following aspects of our general efforts on the characterization of the components and pathways of electron transfer systems will be emphasized in 1974/75: 1. Characterization and identification of two yet unknown electron acceptors which have been recognized in the EPR spectra. 2. Kinetic studies with EPR spectroscopic observation of the reoxidation reactions of reduced succinate dehydrogenase and cytochrome oxidase and of membrane-bound iron-sulfur proteins in general. 3. Correlation of biogenesis and degradation of phosphorylation Site 1 with that of iron sulfur centers in yeast. 4. Development of a workable system for rapid mixing at 0 to -50 degrees C, and freezing of reactants for EPR spectroscopic for EPR spectroscopic and optical observation.